1. Field of the Invention
The present invention relates to testing method and apparatus of a thin-film magnetic head with a magnetoresistive effect (MR) read head element having a multi-layered structure that includes a magnetization-fixed layer and a magnetization-free layer.
2. Description of the Related Art
As hard disk drive apparatuses (HDD) increase in capacity and reduce in size, highly sensitive and high-output thin-film magnetic heads are being demanded. In order to satisfy the demand, performance of giant magnetoresistive effect (GMR) thin-film magnetic heads with GMR read head elements are being improved. On the other hand, tunnel magnetoresistive effect (TMR) thin-film magnetic heads with TMR read head elements having a magnetoresistivity ratio more than twice as high as that of the GMR thin-film magnetic heads are being developed.
Among the thin-film magnetic heads with such GMR or TMR read head elements having a multi-layered structure, some heads may produce noises when their environment temperature becomes high. Thus, after fabricating the thin-film magnetic heads, it is necessary to check that the fabricated heads never produce such noises or high-temperature noises.
FIGS. 1a and 1b illustrate non-signal output versus frequency characteristics of a good thin-film magnetic head providing no high-temperature noise and of a defective thin-film magnetic head providing high-temperature noises, respectively. In these figures, lateral axis indicates frequency (MHz) and longitudinal axis indicates non-signal output represented by power, namely noise (dBm). In this case, a low temperature corresponds to −10° C., a room temperature corresponds to −25-30° C. and a high temperature corresponds to 85° C.
Since the noise hardly changes depending upon the temperature change, the thin-film magnetic head corresponding to FIG. 1a is a good element providing no high-temperature noise. Contrary to this, since the noise increases when the temperature increases, the thin-film magnetic head corresponding to FIG. 1b is a defective element providing high-temperature noises.
Generally, in order to check whether a thin-film magnetic head produces high-temperature noises or not, it is necessary to measure a noise level in an output signal from the thin-film magnetic head under a condition where its environment temperature is actually increased to a high temperature. However, increasing in the environment temperature of the thin-film magnetic head from a room temperature to a high temperature at each measurement takes much expense in time and effort, and therefore the check procedure becomes extremely complicated and the check time becomes much long.